85,026 research outputs found
Statistical Physics in Meteorology
Various aspects of modern statistical physics and meteorology can be tied
together. The historical importance of the University of Wroclaw in the field
of meteorology is first pointed out. Next, some basic difference about time and
space scales between meteorology and climatology is outlined. The nature and
role of clouds both from a geometric and thermal point of view are recalled.
Recent studies of scaling laws for atmospheric variables are mentioned, like
studies on cirrus ice content, brightness temperature, liquid water path
fluctuations, cloud base height fluctuations, .... Technical time series
analysis approaches based on modern statistical physics considerations are
outlined.Comment: Short version of an invited paper at the XXIth Max Born
symposium,Ladek Zdroj, Poland; Sept. 200
Information in statistical physics
We review with a tutorial scope the information theory foundations of quantum
statistical physics. Only a small proportion of the variables that characterize
a system at the microscopic scale can be controlled, for both practical and
theoretical reasons, and a probabilistic description involving the observers is
required. The criterion of maximum von Neumann entropy is then used for making
reasonable inferences. It means that no spurious information is introduced
besides the known data. Its outcomes can be given a direct justification based
on the principle of indifference of Laplace. We introduce the concept of
relevant entropy associated with some set of relevant variables; it
characterizes the information that is missing at the microscopic level when
only these variables are known. For equilibrium problems, the relevant
variables are the conserved ones, and the Second Law is recovered as a second
step of the inference process. For non-equilibrium problems, the increase of
the relevant entropy expresses an irretrievable loss of information from the
relevant variables towards the irrelevant ones. Two examples illustrate the
flexibility of the choice of relevant variables and the multiplicity of the
associated entropies: the thermodynamic entropy (satisfying the Clausius-Duhem
inequality) and the Boltzmann entropy (satisfying the H-theorem). The
identification of entropy with missing information is also supported by the
paradox of Maxwell's demon. Spin-echo experiments show that irreversibility
itself is not an absolute concept: use of hidden information may overcome the
arrow of time.Comment: latex InfoStatPhys-unix.tex, 3 files, 2 figures, 32 pages
http://www-spht.cea.fr/articles/T04/18
Homotopy in statistical physics
In condensed matter physics and related areas, topological defects play
important roles in phase transitions and critical phenomena. Homotopy theory
facilitates the classification of such topological defects. After a pedagogic
introduction to the mathematical methods involved in topology and homotopy
theory, the role of the latter in a number of mainly low-dimensional
statistical-mechanical systems is outlined. Some recent activities in this area
are reviewed and some possible future directions are discussed.Comment: Significant extensions and updates: 29 pages, 11 figures. Lecture
given at the Mochima Spring School, Mochima, Venezuela, June 2006. To appear
in Cond. Matt. Phy
Statistical Physics of Structural Glasses
This paper gives an introduction and brief overview of some of our recent
work on the equilibrium thermodynamics of glasses. We have focused onto first
principle computations in simple fragile glasses, starting from the two body
interatomic potential. A replica formulation translates this problem into that
of a gas of interacting molecules, each molecule being built of atoms, and
having a gyration radius (related to the cage size) which vanishes at zero
temperature. We use a small cage expansion, valid at low temperatures, which
allows to compute the cage size, the specific heat (which follows the Dulong
and Petit law), and the configurational entropy. The no-replica interpretation
of the computations is also briefly described. The results, particularly those
concerning the Kauzmann tempaerature and the configurational entropy, are
compared to recent numerical simulations.Comment: 21 pages, 6 figures, to appear in the proceedings of the Trieste
workshop on "Unifying Concepts in Glass Physics
Statistical Physics of Self-Replication
Self-replication is a capacity common to every species of living thing, and
simple physical intuition dictates that such a process must invariably be
fueled by the production of entropy. Here, we undertake to make this intuition
rigorous and quantitative by deriving a lower bound for the amount of heat that
is produced during a process of self-replication in a system coupled to a
thermal bath. We find that the minimum value for the physically allowed rate of
heat production is determined by the growth rate, internal entropy, and
durability of the replicator, and we discuss the implications of this finding
for bacterial cell division, as well as for the pre-biotic emergence of
self-replicating nucleic acids.Comment: 4+ pages, 1 figur
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